Optical fiber with quantum dots

ABSTRACT

Holey optical fibers (e.g. photonic fibers, random-hole fibers) are fabricated with quantum dots disposed in the holes. The quantum dots can provide light amplification and sensing functions, for example. When used for sensing, the dots will experience altered optical properties (e.g. altered fluorescence or absorption wavelength) in response to certain chemicals, biological elements, radiation, high energy particles, electrical or magnetic fields, or thermal/mechanical deformations. Since the dots are disposed in the holes, the dots interact with the evanescent field of core-confined light. Quantum dots can be damaged by high heat, and so typically cannot be embedded within conventional silica optical fibers. In the present invention, dots can be carried into the holes by a solvent at room temperature. The present invention also includes solid glass fibers made of low melting point materials (e.g. phosphate glass, lead oxide glass) with embedded quantum dots.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority from co-pendingprovisional applications 60/476,650 filed on Jun. 9, 2003 and60/543,620, filed on Feb. 12, 2004, the complete contents of which areherein incorporated by reference.

FIELD OF THE INVENTION

The present invention provides optical fibers (holey fibers or lowmelting point glass fibers) containing quantum dots. The presentinvention relates generally to fiber-based sensors, lasers, modulators,wavelength converters, filters, linear and non-linear elements.

BACKGROUND OF THE INVENTION

Quantum dots are nanometer-scale particles (e.g., typically 1–10nanometers in diameter) of metal, dielectric or semiconductor material.Quantum dots are commonly made of compound semiconductors such as CdSe,ZnSe, or PbS and may be manufactured in solid hosts, films, suspensionsor other material formats.

Quantum dots are well known for providing useful optical properties whenincorporated into polymeric and glass materials. Specifically, quantumdots can provide optical amplification, saturable absorption, ornonlinear effects for example. As understood in the art, the termquantum dot may apply to particles in the form of spheres, rods, wires,etc. The term ‘quantum dot’ herein refers to any such forms as are knownin the art.

U.S. Pat. No. 5,881,200 to Burt, for example teaches an optical fiberwith a hollow core filled with a quantum dot colloid. The quantum dotsprovide an optical gain medium that can be used as a laser amplifier.Similarly, U.S. Pat. No. 5,260,957 to Hakimi et al. teaches a polymericoptical waveguide containing quantum dots that provide lasingcapability. U.S. Pat. No. 6,710,366 also teaches matrix compositematerials with quantum dots having nonlinear optical properties.

Incorporating quantum dots into optical fibers and waveguides can beproblematic because of the sensitive nature of quantum dots. Forexample, many quantum dots are not able to withstand high temperatures(e.g., above 1000 C) required for melting glass or silica. Specifically,quantum dots from compound semiconductors can dissociate or diffuse intoglass at high temperatures. Quantum dots typically cannot be directlyincorporated into a silica optical fiber because they will be destroyedduring the high heat (e.g. 1500 C) drawing process. Also, quantum dotscan be damaged by oxidation.

Many quantum dots provide superior electronic and optical propertieswhen they are coated with a core shell material such as TOPO. Such coreshells can prevent oxidation and enhance electron confinement, and mayeven be essential in some applications. However, core shell materialsare often polymeric and are often destroyed by high temperatures.

However, there are many potential applications for optical fibers(particularly glass fibers) having quantum dots. It would be an advancein the art to provide glass optical fibers having quantum dots thatretain desirable electronic and optical properties unaltered by highheat. Additionally, it would be an advance in the art to provide newoptical fiber structures and materials that are compatible with quantumdots and with conventional optical fibers.

SUMMARY OF THE INVENTION

The present invention includes a holey optical fiber having a pluralityof holes that provide light confinement. A plurality of quantum dots aredisposed within the holes. The quantum dots provide wavelengthconversion, amplification, fluorescence, absorption, lasing and otherlinear and non-linear functions to the fiber.

The fiber can be a regular or irregular array holey fiber, a photoniccrystal fiber, an index-guiding fiber, a random-hole holey fiber, orcombinations thereof, for example. The holes can be disposed in thecladding, both the core and cladding, or a plurality of cores andcladdings with a plurality of geometric cross-sections.

The quantum dots can be suspended in a solvent that is also disposed inthe holes. Alternatively, there is no solvent, and the quantum dots resupported by sidewalls of the holes. The quantum dots can preferablyhave diameters in the range of about 0.5–100 nanometers.

The present invention also includes an optical fiber made of glasshaving a drawing temperature less than 700 Celsius, and having quantumdots embedded in the glass. The glass can be a phosphate glass or a leadglass (e.g. comprising more than 40% phosphate or lead). The glass mayalso have a drawing temperature less than 500 Celsius.

The quantum dots can be disposed in the core, the cladding or both.

The present invention also includes a method for making holey opticalfibers with quantum dots disposed in the holes. In the present method,the holey optical fiber is submerged in a colloid or suspension ofquantum dots in a solvent. The quantum dots are drawn into the holes bycapillary action. A cut end of the holey fiber may be submerged in thequantum dot colloid.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a cross sectional view of a random hole holey fiber withquantum dots according to the present invention.

FIG. 2 shows a photonic crystal holey fiber with quantum dots accordingto the present invention.

FIG. 3 shows a random hole holey fiber with holes in the core containingquantum dots according to the present invention.

FIG. 4 shows an index-guiding holey fiber containing quantum dosaccording to the present invention.

FIG. 5 shows a generalized fiber sensor according to the presentinvention.

FIG. 6 shows a random hole holey fiber with the holes exposed to theenvironment. Exposed holes tend to increase sensor sensitivity,particularly in chemical sensing applications.

FIG. 7 illustrates a preferred method for making the present quantum dotoptical fibers.

FIG. 8 shows a solid optical fiber having embedded quantum dots, andmade of a low melting point glass.

FIG. 9 illustrates a method for making random hole holey optical fiber.

FIG. 10 shows a holey optical fiber with quantum dots according to thepresent invention fusion-spliced to a conventional solid fiber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present invention provides optical fibers having quantum dots. Thefibers are holey fibers and can be photonic fibers, index guiding holeyfibers, or random-hole holey fibers. In the present invention, thequantum dots are incorporated into the holes of the holey fibers. Theholes can be in the cladding or core of the fiber. Even if the quantumdots are disposed in the cladding, where core-confined light exists asan evanescent wave, the quantum dots interact strongly with guided lightand can provide amplification, sensing and other functions. The quantumdots can be inserted into the fiber by flowing a colloid or suspensionof the quantum dots into the holes of the fiber. The colloid can flowunder the influence of capillary forces or via other entrainment methodssuch as vacuum, thermal or mechanical means, and/or combinations of suchmeans. Retention of the quantum dots may be accomplished by capillaryforce, splicing to conventional optical fibers, or conversion of thesolvent to solid or gelatinous forms, for example.

In an alternative embodiment, the fibers can be made of low meltingpoint glasses (e.g., lead glasses, phosphate glasses) having a workingtemperature (suitable for fiber drawing) less than 700C, 600C or 500C.Many quantum dot materials can survive temperatures in the range ofabout 400–700C.

FIG. 1 shows a cross section of a random-hole holey fiber with quantumdots according to the present invention. The fiber has a solid core 20surrounded by a cladding 22 containing a large number of randomlyarranged holes 26. A solid sheath 24 surrounds the cladding 22. In thepresent invention, quantum dots 28 are disposed within the holes 26. Thequantum dots are illustrated as small rectangles or dots.

The fiber can be made of silica, alumina (sapphire), ceramics,borosilicate glass, polymers, plastics or any other known fibermaterial.

The random holes 26 can have diameters in the range of tens of micronsto less than a micron. The random holes can have lengths of millimeters,meters or kilometers, for example. Preferably there are hundreds ofrandom holes in the fiber. Total required hole cross-sectional arearelative to the rest of the fiber is dependent on the specificapplication or effect to be generated. The random hole fiber can be madeby preform methods such as sol-gel processes, glass foam processes or byincorporating a gas generating material into a glass fiber perform (asexamples), and then drawing the fiber from the resulting preform. FIG. 9illustrates a method for making random-hole optical fiber based on thelatter technique as an example. In the method, a fiber preform comprisesa silica tube 50 filled with a holey region forming powder 52 and asolid silica rod 54. The holey region forming powder 52 forms a fibercladding and the solid rod 54 forms a fiber core. Heaters 56 heat thepreform so that it can be pulled to form a fiber 58, as known in theart.

The holey region forming powder 52 preferably comprises a mixture of aglass material (e.g., high purity silica powder) and a gas-generatingmaterial (e.g., silicon nitride). The gas generating material produces agas when heated above the sintering temperature of the glass material.The gas generating material can produce gas by thermal decomposition orby chemical reactions (e.g., oxidation) with other components of theholey region forming powder, for example. The gas generated within theholey region forming powder 52 forms trapped bubbles 60 as the holeyregion forming powder 52 sinters and softens. The bubbles 60 arestretched and drawn into elongated tubes 62 as the fiber 58 is pulled.In preferred embodiments, the glass material is silica, and the gasgenerating material is a nitride or carbide ceramic. Alternatively, thegas generating material can be a metal nitrate or metal carbonate (e.g.sodium nitrate or sodium carbonate). If silicon nitride is used as thegas generating material, it can be added in amounts of about 0.01–0.5%by weight. The method for making random hole fibers is also described inthe paper “Microstructural Analysis of Random Hole Optical Fibers” byPickrell et al., IEEE Photonics technology Letters, Vol. 16, No. 2,February 2004, which is hereby incorporated by reference.

The quantum dots 28 can be made of many materials including 2–6 and 3–5compound semiconductors, tertiary compound semiconductors, germanium,silicon, ceramics, dielectrics, metals and the like as in known in theart. Specific examples of possible materials for the quantum dotsinclude ZnS, ZnSe, ZnTe, ZnO, CdS, CdSe, CdTe, CdO, HgS, HgSe, HgTe,HgO, MgS, MgSe, MgTe, MgO, CaS, CaSe, CaTe, CaO, SrS, SrSe, SrTe, SrO,BaS, BaSe, BaTe, BaO, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN,InP, InAs, InSb PbS, PbSe, PbTe, PbO and mixtures thereof. Cadmiumselenide is particularly useful because it has desirable opticalproperties such as fluorescence and light amplification in the visibleto near infrared optical spectrum. Quantum dots may be combinations ofthe foregoing materials and may include core-only configurations orcombined in core-shell configurations with polymer or non-polymericshells. Shell materials can range from polymers such as TrioctylPhosphine Oxide (TOPO) to non-polymeric such as ZnS as are known in theart.

The quantum dots can have diameters typically between 1 and 10 nm or 1and 100 nanometers. The size of the dots will depend upon theapplication of the present optical fiber, the quantum dot configuration(i.e., core only, core shell, etc.) and the wavelength range to beaddressed. A plurality of dot sizes may be employed to achieve arbitrarywavelength spectral effects as appropriate to the nature of the quantumdot materials. A wavelength range from 0.3 microns to beyond 2 micronsis addressable in the optical fibers disclosed herein.

The quantum dots can be suspended in a liquid solvent within the holes26. The solvent can be toluene, heptane, chloroform, xylene, acetone,hydrocarbon alcohols or the like. The quantum dots can be freelyfloating in the solvent, or can be supported by the sidewalls of theholes 26 (e.g., by Van der Waals forces). As noted, the quantum dots canbe coated with a capping material such as TOPO, as known in the art, orcan be uncoated (i.e. bare). Further, the quantum dot structure mayinclude other molecular or atomic attachments such aschemical/biological ligands, functional molecules, etc. as are known inthe art.

Compatible solvents may have an index of refraction greater or less thanthat of the optical fiber material into which they are entrained,depending on the functional effect to be achieved in the over-alloptical fiber structure. Preferably, however, the solvent has arefractive index lower than the refractive index of the glass. As anexample, quantum dots arranged in a high index solvent may enable totalcore confinement in random fiber core structures. Further, solvents maybe used that transition to a solid state with processing or catalysis.As an example, low viscosity polymeric adhesives that transition to asolid state on exposure to UV or other wavelengths of light may be used.

FIG. 10 shows one embodiment of the invention including a holey opticalfiber with quantum dots 28 in holes 26, where the holey optical fiber isfusion-spliced at joint 74 to a conventional solid fiber composed ofcore 70 and 72. This embodiment demonstrates use of the holey opticalfiber in conjunction with other fibers, as may occur in some sensorapplications, etc.

FIG. 2 shows another embodiment of the invention having a photonic holeyfiber. Photonic holey fibers are well known in the art. Photonic holeyfibers have a regular array pattern of holes 26. The photonic holeyfiber is typically made by stacking a bundle of hollow glass tubes toform a fiber preform, and then drawing the preform into a fiber. In thephotonic holey fiber of FIG. 2, quantum dots 28 are disposed within theholes 26 comprising the photonic crystal lattice. The quantum dots canbe suspended in a solvent or supported on the sidewalls of the holes 26.Sidewall attachment may be augmented with prior processing steps inwhich the wall material is treated to enhance quantum dot attachment viachemical or atomic bonding between the wall or wall impregnatedmaterials and the quantum dot structure.

Quantum dot concentrations may vary substantially depending on theapplication, strength of light coupling in the materials and theinteraction length to be employed. As examples, a filter may employquantum dot concentrations less than 1% by volume, where lasingapplications typically require concentrations of greater than 0.2% andprefer concentrations of greater than 1% by volume. Concentrations incoherent applications are also dependent on the diameter and length ofthe micro-cavities formed by the entrained holes. Smaller diameters(e.g. less than 20 um), for instance, enhance micro-cavity effects (e.g.lasing) for lower concentrations of quantum dots.

In operation, the quantum dots interact with light traveling through thecore 20 of the fiber. The interaction can result in light amplification,fluorescence, wavelength-shifting, nonlinear optical effects, orenvironmental sensing (including radiation fields from nuclear or cosmicbombardment). Although the quantum dots are located within the holes 26,where light might exist only as an evanescent wave, the quantum dots areable to interact with light in the core and provide their effects. It isnoted that the quantum dots can interact with light propagating in thecore by coherent and/or incoherent scattering coupling mechanisms.

For example, in one experiment performed by the present inventors, aphotonic holey fiber like the fiber of FIG. 2 has holes filled with acolloid of CdSe quantum dots in heptane (e.g. with a volumeconcentration of 0.2% or more). When 488 nm pump radiation is injectedinto the fiber core, a co-propagating 594 nm signal beam travelingthrough the core experiences a power gain of 100% over a distance of 10cm from evanescent field coupling of both pump and signal to the quantumdots. The CdSe quantum dots absorb the 488 nm energy and provide opticalamplification at 594 nm. The quantum dot materials had been held in theexperimental fiber for in excess of a year via capillary forces alone.

It is noted that random hole holey fibers are particularly well suitedfor use with quantum dots according to the invention. Specifically, thisis because random hole holey fibers tend to have some holes that extendto the core region of the optical fiber, where light intensity isgreatest. As a result, the quantum dots located close to the coreinteract strongly with core-confined light.

FIG. 3 shows another embodiment of the present invention in which thecore 20 includes holes 30. The core holes 30 may contain quantum dots.The core 20 in this embodiment has a lower porosity than the cladding 22so that light is confined to the core 20. The fiber of FIG. 3 can be arandom hole holey fiber made from a preform having gas generatingmaterial incorporated into the core and/or cladding region of thepreform. An advantage of having core holes 30 with quantum dots is thatthe quantum dots are located in a region of high light intensity (evenif they are exposed to only an evanescent wave), and so will interactstrongly with light across the core 20.

FIG. 4 shows an embodiment of the invention in which the holey opticalfiber is an index-guiding holey fiber, as known in the art. In thiscase, the optical fiber does not have a regular crystalline pattern ofholes like the fiber of FIG. 2. In the present invention, Quantum dots28 are disposed within the holes 26 of the index-guiding holey fiber.Methods for making index-guiding and photonic crystal holey fibers arewell known in the art. Typically, solid rods and hollow tubes arestacked to form a fiber perform, which is then heated and drawn into athin fiber. U.S. Pat. No. 5,155,792 to Vali et al. and U.S. Pat. No.5,802,236 to DiGiovanni et al. describe methods for makingmicrostructured optical fibers, and are hereby incorporated by referencein their entirety.

As is well known in the art, in conventional optical fibers, themicrostructure of the fiber consists of a core region surrounded by aclad region. Holey fibers generally consist of a more complex mixture ofcore(s) and clad regions with interspersed holes, the totality of whichis referred to herein as the fiber's microstructure. In conventionaloptical fibers, the core of the fiber has a higher index of refractionthan the clad region leading to light guiding in the core via totalinternal reflection due to the index difference as noted. In this sense,the guiding region of the fiber is comprised of essentially the core. Inholey fibers entrained with quantum dot bearing solvents, the index ofthe solvent relative to the index of the surrounding microstructuredetermines the guiding region or regions. For example, if the index ofthe solvent is uniformly lower than that of the glass microstructure ina uniform index glass holey fiber, the entire glass microstructurebecomes the guiding region. If the index of the solvent is higher thanthe glass in this example, the solvent containing regions would becomethe guiding region. The guiding region would include or exclude theregion conventionally designated as the core(s) of the microstructure onthe basis of the index difference. Depending on microstructure details,quantum dot holey fibers may use any portion of the total microstructureas the guiding region.

The present quantum dot holey fibers can be used in a wide range ofsensing applications. Quantum dots have electronic structures andoptical properties that respond to a variety of chemical and physicalenvironmental changes. For example, the present fibers can be used in pHand chemical sensors, pressure or force sensors, electric field sensors,magnetic field sensors, and temperatures sensors. Typically, sensorsbased on the present quantum dot holey fibers will operate to detect anoptical characteristic such as a shift in fluorescence, lasing orabsorption wavelength or intensity of the quantum dots. Such effects mayarise from linear or non-linear optical properties. FIG. 5 shows ageneralized fiber sensor according to the present invention. The sensorhas a holey fiber 32 containing quantum dots. The fiber is connected toa light emitter and an optical detector. The light emitter can producesingle wavelengths or a broad spectrum of wavelengths. The opticaldetector detects changes in absorption, lasing or fluorescence in theoptical fiber caused by interactions of the quantum dots with theenvironment. The optical detector can be a spectrophotometer, forexample.

If the index of the solvent is lower than that of the glass material,light may be guided by, and therefore confined to either the regionaround the holes represented by the core or the region surrounding holesrepresented by the cladding structure. If the fiber is coated with a lowindex coating instead of the high index clad typically used to strip offcladding modes, the cladding mode light will form effective light forsensor operations. This concept is very useful for all kinds of sensors,in that it preserves light for signal to noise ratio enhancements andpreserves a larger fraction of the fiber sensor's cross-section forinteraction with the environment.

Also, it is noted that in the sensor embodiments, the solvent can have ahigher or lower refractive index than the glass.

Following is a list of considerations for making different types ofsensors:

pH sensor: In a pH sensor according to the present invention, quantumdots are selected that change optical properties when exposed to H+ ionsor OH− ions. Examples of such quantum dots include the CdSe/ZnScore-shell dots which have been used for proof of principle tests. Inuse, the fiber is submerged in a liquid to detect the pH. H+ ionsdiffuse through the glass and come in contact with the quantum dots,thereby affecting their fluorescence, absorption, lasing or otheroptical characteristics. To enhance the sensitivity, and make the fibercapable of sensing species that cannot diffuse through glass (e.g.,OH−), the fiber can be designed to lack the solid sheath 24. The solidsheath 24 can be removed by etching, or the fiber can be drawn withoutthe solid sheath. Such a fiber is illustrated in FIG. 6.

Chemical/Biological sensor(s): In a chemical, biological, orbio-chemical sensor, the quantum dots can be chemically bound oressentially “coated” with a material (e.g. a polymer, biologicalmaterial, ceramic or metal) that changes the optical properties of thequantum dot when it comes in contact with a chemical to be detected. Forexample DNA ligands or bio-hazard molecules. In this case, the speciesor element to be detected can be injected or diffused into the holes 26,via molecular diffusion, capillary action or other means appropriate tothe state and structure of the fiber-quantum dot sensor. Alternatively,the fiber can be processed (e.g. chemically etched, mechanically abradedor cut open) so that the holes are opened to the outside world and thechemical to be detected can flow into the holes 26 again via moleculardiffusion, capillary action or other means appropriate to the state andstructure of the fiber-quantum dot sensor. For example, biomoleculesdissolved or dispersed in water can be detected by submerging a cutfiber end in the water, and allowing the biomolecules to diffuse intothe holes. One advantage to this technique is that the requisite amountof sample for analysis is in the range of nano to microliters. Thisallows analyte solutions to remain essentially undiminished in volume.

Force/strain sensor: Quantum dots supported or adhered to the sidewallsof the holes 26 are sensitive to the electronic state or atomic energystates of the sidewall. This is particularly true if the quantum dotlacks a coating (e.g. TOPO) or the coating of the quantum dot and wallare chosen to enhance any surface energy interactions. As a result ofinteractions between the quantum dots and sidewall energy states, theelectronic structure and optical properties of the quantum dots will bealtered by strain in the fiber material matrix. Hence, the strain orforce can be detected by monitoring the optical characteristics of thequantum dots. Wavelength shifts up to 15 nm are readily observed betweenthe fluorescent emission peaks of bulk CDSe/ZnS quantum dot-heptanecolloids in a beaker and the same material entrained in holey fiberstructures with a plurality of 6–14 um diameter holes. Wavelength shifts(35 nm) are likewise noted down the length of such fibers due toemission/re-absorption/filtering effects that may be modulated withmicro-bending of the optical fiber.

Electric field/magnetic field sensor: it is well known that theelectronic structure and optical properties of quantum dots can bealtered by electric or magnetic fields. Electric and magnetic fields canbe detected by monitoring changes in absorption, lasing, fluorescence orother characteristics of the quantum dots.

X-ray, Nuclear radiation or particle detection: it is well known thatthe electronic structure and optical properties of quantum dots can bealtered by encountering X-ray/nuclear radiation or high energyparticles. In particular, such encounters can generate directfluorescent light generation or cause degeneration of the quantum dotmaterial with attendant effects on the materials optical properties.Consequently, quantum dot loaded optical fibers can be used to develop avariety of sensors for direct or remote sensing of radiation parameters.

Wavelength conversion sensors and fibers: Use of embedded quantum dotsin a cascade of response characteristics from shorter wavelengths tolonger wavelengths enables the use of conventional detectors and filterelements sensitive to longer wavelengths for sensing short wavelengthradiation. Such wavelength conversion could be enabled by the ordinaryabsorption/emission characteristics of the quantum dots or higher leveloptical properties such as Brillioun and Raman scattering. For example,a holey fiber embedded with quantum dots which absorb at UV wavelengthsbelow 350 nm and re-emit at wavelengths above 400 nm may be used withconventional silicon detectors instead of the less sensitive, moreexpensive extended response silicon detectors. Longer wavelength filterelements may also be used in this technique to enhance signal to noiseratio or other signal properties. Similarly, a mixture of quantum dotsin varying sizes may broaden the absorption and emission band to allowdetection of X-ray or nuclear radiation by conventional silicondetectors in replacement of conventional scintillation detectors. Ineach case, some portion of the light absorbed by the quantum dots isemitted at longer wavelengths to be sensed and/or filtered by detectorsand filters whose performance characteristics peak at the longerwavelengths.

FIG. 7 illustrates a method for making the present quantum dot holeyfibers. In the preferred method, a cut end 36 of a holey optical fiberis submerged in a colloid or suspension of quantum dots in a solvent.Alternatively, a sidewall of the fiber is etched, abraded or otherwisecut open to expose some of the holes 26, and the sidewall with exposedholes is submerged. Under the influence of capillary forces, the solventis drawn into the holes of the holey fiber. The solvent can be heptane,xylene, or other hydrocarbons or alcohols, for example. Depending onhole size, solvent combinations and capillary assist methodology thecolloid can travel millimeters to kilometers into the holey fiber. Highvapor pressure solvents (low viscosity) will generally travel furtherinto the optical fiber than low vapor pressure solvents. If the holesare too small (e.g. submicron size) some solvents might not be drawninto the holes without assistance. The hole size should be selected inview of the solvent to be used, the surface properties of the holes, andthe desired distance for the quantum dots to be drawn into the fiber andthe desired optical effect.

Capillary forces can result in long duration containment of the quantumdots. Capillary forces have been demonstrated to hold entrained quantumdots for storage times in excessive of two years in proof of principleexperiments. Also, the ends of the fiber can be fused or melted (e.g.with a fusion splicer) so that the holes are sealed shut at the ends.Further the holey fiber can be fused to solid fibers both for sealingand connection into conventional fiber networks.

Optionally, the solvent can be removed (e.g., by vacuum evaporation)after the quantum dots have been inserted into the fiber. Also, thefiber can be submerged for a short duration (e.g., less than 1 second)so that the quantum dot colloid only travels a short distance. Theresulting holey fiber with localized quantum dot distribution can beused as a sensor with localized sensitivity, for example. Quantum dotpenetration may alternately be limited via other means, includingmechanically induced blockages, splicing to solid element fibers andother methods as are obvious to those skilled in the state of the art.

FIG. 8 shows another embodiment of the invention in which the opticalfiber is solid glass and contains embedded quantum dots. The fiber has acladding region 42 and a core 44. The core 44 and cladding 42 bothcontain quantum dots 28. Alternatively, only the cladding or corecontains quantum dots. Significantly, the fiber is made of a low-meltingpoint glass that can be drawn into a fiber at temperatures that do notdamage the quantum dots 28. For example, the fiber can be made ofphosphate glasses (e.g. at least 25% phosphate), lead glasses orchalcogenide polymers, which can be drawn into a fiber at temperaturesin the range of 300–700 degrees Celcius. Preferably, the fiber is madeof a glass that can be drawn at a temperature less than 700 C, 600 C,500 C or 400 C. The sheath, cladding and core can all be made of thesame glass. The core 44 should have a dopant or slightly differentcomposition so that it has a higher refractive index than the cladding,as well known in the art.

Of course, the quantum dots used must be resistant to the temperaturesused to draw the optical fiber. Examples of suitable, heat-resistantquantum dot materials include tellurides, antimonies and CdSe since ithas a boiling point between 600 and 700 degrees C. (depending onconfinement conditions). In general, the quantum dot material shouldhave a boiling point lower than the drawing temperature of the glass.

The optical fiber of FIG. 8 can be made by incorporating quantum dotsinto a fiber preform, and then drawing the fiber preform into an opticalfiber. The fiber preform can comprise glass powder mixed with quantumdot materials, such as a quantum dot colloid or suspension as is commonin the art with the technique known as solution doping (an extrinsicdoping process). In this technique, a glass frit or power is depositedinternal to a preform tube via chemical deposition or other means. Thequantum dot bearing solvent is then placed in the preform in sufficientvolume to allow the solvent to be entrained into the porous interiorsurface. After residual solvent is removed, the preform is collapsed anddrawn into a fiber as is common in the art. In an alternate embodimentof this technique, the powder material may be impregnated with or boundto the quantum dot-solvent materials and then deposited in the preformas a slurry material). In this regard an extrinsic process is defined asone in which the quantum dots have been formed in a separate processprior to embedding in a final host material. By contrast an intrinsicprocess would form the quantum dots from their constituent materialsduring processing. For example if Cd and Se elements were used to dope aglass preform and the preform processed in such a manner that the CdSequantum dots form on cooling an intrinsic process would be formed.

The optical fiber of FIG. 8 can be used for many applications such aslight amplification, wavelength shifting, saturable absorption, andsensing in accordance with the nature of the structure and materialsused. For example, the fiber of FIG. 8 with embedded quantum dots can beused as a force or strain sensor since the quantum dots will be affectedby strain on the fiber.

It will be clear to one skilled in the art that the above embodiment maybe altered in many ways without departing from the scope of theinvention. Accordingly, the scope of the invention should be determinedby the following claims and their legal equivalents.

1. An optical fiber sensor, comprising: a holey optical fibercomprising: a) a guiding region for carrying confined light b) aplurality of holes in the optical fiber; c) a plurality of quantum dotsin the holes; and a light detector coupled to the holey optical fiber,operable for detecting a change in an optical characteristic of thequantum dots.
 2. The optical fiber sensor of claim 1 wherein a change inelectric or magnetic field causes a change in the optical characteristicof the quantum dots.
 3. The optical fiber sensor of claim 1 wherein achange in exposure to cosmic particles, nuclear or other ionizingradiation causes a change in the optical characteristic of the quantumdots.
 4. The optical fiber sensor of claim 1 wherein a change inchemical, biological or biochemical exposure causes a change in theoptical characteristic of the quantum dots.
 5. The optical fiber sensorof claim 1 wherein a change in mechanical properties in the fiber causesa change in the optical characteristic of the quantum dots.
 6. Theoptical fiber sensor of claim 1 wherein at least some of the holes areopen to the exterior of the fiber.
 7. The optical fiber sensor of claim1 further comprising a radiation source for injecting radiation into thefiber and wherein the quantum dots shift a wavelength of the radiationto longer wavelengths.